Sorry, this will be long, because it will contain all my best tortoise advice!
Google tortoise owner sites. Don't feed it lettuce! (Apparently, they can get nasty gut problems/tumours). I did not find this out for the first 30 years (in fact, I was extremely ignorant about tortoise care, as were most people, and it wasn't easy to find out). The best thing for tortoises is to be able to roam safely in your garden and eat food that they forage themselves (you can supplement with stuff - mine LOVED apricots and buttercup flowers) - so leave dandelions and other wild plants growing, if you can (you can find out by googling which ones they can/like to eat - I remember there was something called sow thistle). Very, very important, make your garden absolutely secure - they can burrow under things a bit, they can climb fences if there are enough protruberances for footholds (my friend knew someone who looked out of her window and saw a tortoise entering her garden over a six-foot fence). For a lot of years (because he could escape our large garden quite easily) ours lived in a fairly small wooden pen that my father made. He was pretty unhappy, I thought and I was right because, years later, when my mother moved somewhere where I could tortoise-proof a large section of garden, he was free to roam again and his personality perked up amazingly (he was still a bit dour, though!).
Get it microchipped in case it goes AWOL. We lost ours on numerous occasions - in the early years he had our address painted on his shell but I now know you should not do that as putting stuff on the shell may seriously affect their health. A motorcyclist saw a rock in the road once, which turned out to be our tortoise (lucky the address was still on then). In later years, he disappeared once for three whole weeks. Eventually, someone who saw our posters said they'd found him and sent him to live with their sister a few miles away (who had a walled garden) until they could reunite him.
Read up about hibernating it. We used to be told to put it in a box with hay in and ours couldn't get off to sleep because it was too hot so my father ended up putting it in a box full of dry leaves (newspaper at the bottom)inside a bigger cardboard box (I think the gaps being stuffed with newspaper) and the whole thing was in our unheated garden shed. There is lots to learn about them - ours was a spur-thighed European tortoise, I think - we had him 45 years but he then had a bad hibernation. He went to sleep after a period of poor autumn weather so hadn't eaten enough and, although he did wake up in the spring, he was not very mobile and the weather wasn't super warm so he didn't want to eat so he didn't make it.
They need a shallow dish of water that they can get in and out of - they appreciate daily wallow in this and it helps to keep them well hydrated - they drink a great deal and give themselves a "washout" (so it needs cleaning every day, if not twice a day).
It is a bit difficult finding someone to look after them for holidays Neighbours are not much good, however willing, as tortoises, when actively roaming about, often tip themselves over and can't get up again so you have to check them several times a day, if possible, to make sure they are not upside down (if left too long, they can die this way). It is unreasonable to expect a neighbour to pop in more than twice a day (i.e. to feed and to make sure they are safely in bed - my tortoise had a little house he would go to at the end of each day - in the second place I lived in he dug himself a cave under a paving stone and used that but we did go and feel to make sure he'd got to bed OK - if not, we had to search the garden for him. Through the net I found an amazing lady near Sevenoaks, who had loads of tortoises and took him for holiday boarding (she also taught me a lot more about tortoise care). I live in London so it was a bit of a trek on the train after work to drop him off but she was great. This was years ago so I doubt she is still doing it.